Lignin is a collective name for a complex aromatic heteropolymer of monolignol (hydroxycinnamyl alcohols), usually derived from phenylalanine in a multistep process. (Whetten, R. and Sederoff, R., (1995) Lignin Biosynthesis, Plant Cell, 7, pp. 1001-1013). These polymers, deposited primarily in cell walls, ensure the necessary mechanical strength of plant stems and most importantly, the hydrophobicity of a plant's vascular tissues. (Vanholme, R. et al. (2010) Lignin biosynthesis and structure, Plant Physiol, 153, pp. 895-905). Due to its hydrophobic nature, lignin serves as a major component of the vascular tissues and plays an essential role in water transport. In addition to its structural and transport-oriented role, lignin is a key component of a plant's defense system. (Goujon, T. et al. (2003) Genes involved in the biosynthesis of lignin precursors in Arabidopsis thaliana, Plant Physiology and Biochemistry, 41, pp. 677-687). Not surprisingly, environmental conditions influence the amount of lignin deposited. (Boerjan, W. et al. (2003) Lignin biosynthesis, Annu Rev Plant Biol, 54, pp. 519-546). For example, lignin biosynthesis is induced in response to various stress conditions like wounding, abiotic stress, and pathogen infection. Lignin limits pathogen invasion and protects the cell wall polysaccharides against microbial degradation. (Vanholme et al., 2010).
A large part of our current understanding of lignin biosynthesis comes from the complete understanding of this pathway in A. thaliana and P. trichocarpa. (Goujon, et al., 2003; Shi, et al. (2010) Towards a systems approach for lignin biosynthesis in Populus trichocarpa: transcript abundance and specificity of the monolignol biosynthetic genes, Plant Cell Physiol, 51, pp. 144-163). There are three basic monolignol monomers: p-coumaryl, coniferyl, and sinapyl alcohols. These monolignols are incorporated into the three lignin units, or building blocks: p-hydroxyphenyl (H), guaiacyl (G), and syringyl (S). See FIG. 1. These monolignols differ in the number of methoxy groups. P-hydroxyphenyl (H) has no methoxy group, guaiacyl (G) has one methoxy group, and syringyl (S) has two methoxy groups. (Goujon et al., 2003). However, in addition to these three monolignols, a few other phenylpropanoids, such as hydroxycinnamyl aldehydes, hydroxycinnamyl esters, and hydroxycinnamyl acetates may also be incorporated. (Boerjan et al., 2003).
After the biosynthesis of these basic lignin building blocks, they are transported to lignifying zones. In the lignifying zones, polymerization occurs by oxidative free-radical-based coupling by peroxidases or laccases and a mesh-like structure is formed by cross-linking with cellulose and hemicellulose. (Boerjan et al., 2003; Vanholme, R. et al. (2008) Lignin engineering, Curr Opin Plant Biol, 11, pp. 278-285). Lignification occurs in different phases during the secondary thickening of the cell wall when the polysaccharide matrix formation is complete. Lignin deposition is influenced by the nature of the polysaccharide matrix. In the primary cell wall, it is found as spherical structures; whereas in the secondary cell wall, it forms lamellae. (Boerjan et al., 2003).
Notwithstanding the indispensable role of lignin in the life of a plant, it is a major limiting factor in the cost-effective/efficient use of plant material in the pulp and biofuel industries. Lignin also limits the use of biomass for fiber, chemical, and energy production. Removal of lignin is a very expensive process and these industries would benefit from access to biomass having less lignin, or a lignin that is easy to degrade. In the last few decades, some understanding of the lignin biosynthetic pathway has been achieved, although portions of the process are not fully understood.
Despite the importance of lignin synthesis to the overall welfare of the jute plant, as well as its impact on several aspects of fiber quality, at present there is no available information detailing lignin biosynthesis in jute. Therefore, a need exists to identify, isolate and utilize genes and enzymes from the jute plant that are involved in the biosynthesis of lignin. The present invention addresses this need.